The invention concerns an aircraft tail region with a cooling system installed in the aircraft tail region, and a method of operating a cooling system installed in the aircraft tail region.
Fuel cell systems make it possible to generate electrical current with low emissions and high efficiency. At present there are therefore efforts to use fuel cell systems in various mobile applications, e.g., in automotive engineering or aviation, to generate electrical energy. For example, in an aircraft, replacing the generators which are currently used for on-board power supply, and are driven by the main engines or auxiliary power units (APUs), with a fuel cell system is conceivable. A fuel cell system could also be used for emergency power supply to the aircraft, and to replace the ram air turbine (RAT) which has been used until now as the emergency power unit.
As well as electrical energy, a fuel cell in operation generates thermal energy, which must be carried away from the fuel cell using a cooling system, to prevent overheating of the fuel cell. A fuel cell system which is used in an aircraft, e.g., for on-board power supply, must be designed so that it is capable of covering a high requirement for electrical energy. However, a powerful fuel cell from the point of view of generating electrical energy also generates a large quantity of thermal energy, and therefore has a high cooling requirement. Additionally, on board an aircraft many further technical devices, which generate heat and must be cooled to ensure safe operation, are provided. These technical devices include, for example, air-conditioning units or electronic control components of the aircraft.
Aircraft cooling systems which are currently used include air inlet openings, which are usually provided in the region of the aircraft outer skin, and which for example can be in the form of ram air inlets, and are used to convey ambient air as coolant into the aircraft cooling system. Cooling air which is heated by receiving heat from devices to be cooled on board the aircraft is usually carried back into the environment through air outlet openings, which are also provided in the region of the aircraft outer skin. However, air inlet openings and air outlet openings which are formed in the aircraft outer skin increase the air resistance, and thus the fuel consumption of the aircraft. Also, aircraft cooling systems which are supplied with cooling air via ram air inlets have high pressure losses, cooling power which is limited among other things by the maximum incoming air volume flow through the ram air inlets, and relatively high weight.
From WO 2010/105744 A2, an aircraft cooling system which is suitable for cooling a fuel cell system, and which includes a cooler with coolant channels through which ambient air can flow, is known. The coolant channels are formed in a matrix body of the cooler, the outer surface of which, when the cooler is fitted in an aircraft, forms an outer surface of the aircraft outer skin. In contrast, an inner surface of the matrix body, when the cooler is fitted in an aircraft, forms an inner surface of the aircraft outer skin. In flying operation of an aircraft equipped with the cooling system, the coolant flow through the coolant channels which are formed in the matrix body of the cooler is controlled so that the coolant enters the coolant channels which are formed in the matrix body in the region of the outer surface of the matrix body, and leaves the coolant channels which are formed in the matrix body in the region of the inner surface of the matrix body. The cooling air is carried out of the aircraft through an opening which is formed in the region of a transom of the aircraft. In contrast, in ground operation of the aircraft the coolant flow is controlled so that cooling air is fed in through the opening which is formed in the region of the transom of the aircraft. The cooling air then flows through the coolant channels which are formed in the matrix body of the cooler, from the inner surface of the matrix body in the direction of the outer surface of the matrix body.